In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving the data rates, system features based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing high-speed data rates, providing low delay and so on, long-term evolution (LTE) has been under study (see, for example, Non-Patent Literature 1).
In an LTE system, there has been proposed a multiple input multiple output (MIMO) system as a radio communication technique for improving a data rate (spectrum efficiency) by transmitting and receiving data with use of a plurality of antennas (see e.g., Non Patent Literature 1). In MIMO transmission, an optimal preceding matrix indicator (PMI) is selected, at the receiver side, from a codebook in which a plurality of phase/amplitude control amounts (precoding matrix (precoding weight)) to be set for the antennas of the transmitter and a plurality of PMIs corresponding to the precoding matrix are defined per rank, and the optimal PMI is fed back to the transmitter. In addition, a rank indicator (RI) indicating the optimal rank is selected and fed back to the transmitter. At the transmitter side, a precoding weight for each transmission antenna is specified based on the PMI and the RI fed back from the receiver, the precoding is performed, and then, transmission information sequences are transmitted.
In the third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in the LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, in the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems to LTE have been under study (for example, LTE Advanced (LTE-A)).